For the first time, second derivative differential electropotentiometry SDEP is applied for detection of oxidationreduction reactions, and is utilized for determination of 1-100 ppm iron(II) pure solutions using 5x10-3-M cerium ammonium sulfate as an oxidant in 1-M sulfuric acid, and a couple of protected platinum electrodes as an indicating system. No excipient was found to pose any interference, thus rendering the method suitable for determination of iron(II) in pharmaceutical preparations. The results of this study were favorably compared statistically with those obtained with the first derivative differential electropotentiometry FDEP method and direct electropotentiometric EP method.